Implantable cardiac stimulation devices, such as pacemakers and/or cardioverter/defibrillators (ICDs), are widely used to monitor and provide therapy for a variety of cardiac arrhythmias. Implantable cardiac stimulation devices generally include one or more implantable sensing/stimulation leads which are typically implanted such that electrodes are in contact with one or more chambers of the patient's heart so as to sense physiologic signals from the heart corresponding to the cardiac activity as well as to provide therapeutic stimulation to the heart when indicated. The electrodes can be configured for dedicated sensing or delivery of therapeutic stimulation or can perform both functions as indicated.
The leads and electrodes are configured in pacing applications for “unipolar” sensing/stimulation when a single electrode of the lead acts as one electrical node with a conductive housing or can of the implantable stimulation device acting as the other electrical node. In both pacing and ICD applications, “bipolar” sensing is employed when separate electrodes of the leads sense between the electrodes themselves rather than between an electrode and a typically more distant case or device housing electrode. Bipolar sensing typically offers the advantage of reduced influence from muscular activity and other far field signals on the signals of interest.
In ICD applications, bipolar sensing can be further distinguished between what is often called “true” bipolar and integrated bipolar sensing. True bipolar sensing is performed between a pair of electrodes, one of which is often strictly a pacing or sensing electrode, e.g. is not used for shock delivery. In integrated bipolar sensing, sensing is performed between a coupled electrode pair (typically the ring and shocking coils) and a small tip electrode. In ICD applications, the terms “unipolar sensing” are often used differently than in pacing applications. In the ICD case, “unipolar sensing” typically means sensing from the tip to the RV coil.
Bipolar configurations are preferred in many applications as they provide more localized sensing adjacent the patient's heart tissue. However, as the sensing electrodes are relatively small and positioned close together, a true bipolar sensing configuration can return a relatively small difference between the sensed magnitudes of the R and T waves such that the implantable stimulation device can more readily erroneously double count on the patient's T waves (FIGS. 9A and 9C) leading to an erroneous tachycardia determination which can result in the delivery of unnecessary and painful shocks. The “integrated bipolar” configuration (as well as the ICD unipolar configuration) generally can provide a significantly increased amplitude of the sensed R wave without proportionately increasing the sensed T wave and thus significantly reduce the likelihood of the implantable cardiac stimulation device double counting on the patient's cardiac activity (FIG. 9B).
However, as one electrode of the integrated bipolar configuration typically has a relatively large surface area and extends much closer to the patient's atrium in an implanted condition, the integrated bipolar configuration tends to more strongly sense the P waves which can also present difficulties in accurately counting the true cardiac activity in certain circumstances. Depending upon the particular configuration of lead(s) employed as well as the physiological morphology of the patient and their particular needs for sensing and stimulation, a true bipolar or an integrated bipolar sensing configuration can provide more effective sensing and stimulation. Thus, a clinician will typically evaluate various configurations of lead sensing as well as placement of the lead(s) at the time of implantation and select the one with the best performance.
However, a preferred sensing configuration can change over time, for example due to a changed interrelationship between the patient's physiology and the implantable lead, and it would be desirable to be able to automatically accommodate such changes to select the lead configuration providing sensing with reduced likelihood of, for example, double counting single cardiac events. It would be further advantageous to have this capability without requiring the direct immediate intervention of the clinician, for example, at a subsequent clinical follow-up, e.g. to have the device respond automatically. It would also be desirable to provide additional sensing configurations that might offer more accurate sensing than known configurations.